Field of the Invention
The present invention relates to a process of manufacturing electronic components by etching and, more particularly, to a process for differential etching two or more predetermined portions of a semiconductor device or printed circuit board by the use of electromagnetic radiation.
In the field of manufacturing electronic components such as semiconductor devices and fine line printed circuit boards, subtractive processes such as mechanical, chemical or dry (e.g., plasma and/or laser) etching are performed either as a batch process, serially or individually. In any of these techniques, a generally uniform etching results.
When a specified portion of a component (a substrate, for example) is to be etched more than another portion, however, the technique heretofore used has been to etch the specified portion for a greater length of time. Alternatively, two or more etchants can be used or mechanical operations performed sequentially to etch the specified portion more than the remaining portion. Thus, a process involving two or more steps has always been required in order to allow one portion of the material to be etched to a greater extent than another portion thereof.
Similarly, providing two different materials on a substrate, each having a unique etching rate, is a conventional technique that results in one-step etching. But there are drawbacks associated with this technique. For example, two or more etching solutions are often required to effect etching of two or more materials. Such a requirement is susceptible to inadvertent mixing of chemical etchants. Only highly sophisticated methods of separating the etchants from one another are effective.
Another challenge, especially in the field of high resolution substrates, is to maintain required tolerances. This problem can require solutions far beyond the limits of present technology. The separate etchants technique can result in inaccurate etching, so that areas not to be etched are, in fact, etched while areas intended to be etched are not.
Numerous examples of laser or laser-assisted etching are taught in the prior art. For example, U.S. Pat. Nos. 4,490,210 and 4,490,211, both issued to Chen et al and assigned to the present assignee, disclose a system for exposing a metallized substrate by laser radiation in a reaction chamber in the presence of a selected gas chosen to react with the metal to be etched.
Laser beam intensity can be adjusted with the use of partially reflecting dielectric mirrors as taught, for example, in U.S. Pat. No. 4,152,072 issued to Hutchings.
The use of so-called masks to select predetermined portions of a substrate to be etched is also known in the art. A mask is a partially opaque structure that prevents electromagnetic radiation of predetermined wavelength(s) or particle bombardment from impinging upon a surface to be etched. U.S. Pat. No. 4,508,749 issued to Brannon et al and assigned to the present assignee, for example, discloses a system for etching polyimide by use of laser radiation. By using a mask between the laser and the polyimide, only parts of the substrate are etched.
The composition and the fabrication of a mask are extremely critical. For use with a given source of electromagnetic radiation, it would be advantageous for the mask to have at least two portions. The reflectivity of a given wavelength of radiation of one portion of the mask should be distinct from the reflectivity of the other portions of the mask.
It would further be desirable for a mask to have three or more different regions of reflectivity so that the substrate created by selective etching can be etched to three or more different levels. This would be especially valuable when used with substrates having a plurality of layers of material. Thus, for a multi-layered substrate, each layer or certain combinations of layers of the substrate could be etched selectively given the correct mask configuration.
Recently, masks with predetermined areas having a dielectric coating of a specified reflectivity property, different than the reflectivity property of a transparent substrate, have been developed. For example, co-pending U.S. patent application, Ser. No. 924,480 filed concurrently by J. R. Lankard et al and assigned to the present assignee titled "High Energy Laser Mask and Method of Making Same," teaches the use of a dielectric to form a mask having a first reflectivity property of the transparent substrate of the mask and a second reflectivity property of a dielectric coating thereon.
Consider a multi-layered substrate having a base layer of chromium on which is disposed a layer of copper on which is further disposed another layer of chromium. The time needed to etch all three layers of this material--called personality etching--with the use of a high intensity laser can be measured and/or calculated. A mask can be fabricated with certain reflectivity characteristics over a portion thereof. In operation, it would be advantageous for a laser beam to etch the entire three layer material personality for one part of the mask in the same time as the top chromium layer alone--called select etching--is being etched through another portion of the mask. Thus, it would be desirable for the combination of three layers of this multi-layered substrate (personality) and the top chromium layer of the substrate (select) to be etched simultaneously and differentially.
It would be advantageous to provide an electromagnetic radiation based system that would allow a material to be etched differentially.
It would also be advantageous to provide a differential etching system that could accomplish such a result in a one-step process.
Moreover, it would also be advantageous to provide a system for etching two or more materials simultaneously by the use of electromagnetic radiation.
It would further be advantageous to provide a system for etching two or more portions of a substrate simultaneously and differentially regardless of whether the portions are composed of the same material.
It would be advantageous to provide a method of simultaneously etching personality and select of an electronic component.
It would further be advantageous to provide a system that would allow electromagnetic radiation to assist in etching a material differentially as a function of position of the material.